MUNICH, Feb 17 (Reuters) - The number two official at the European Commission accused the Polish foreign minister in a heated exchange on Friday of using "alternative facts" to defend Warsaw's controversial judicial changes that Brussels says threaten the rule of law.

"We are really now in alternative fact territory," Frans Timmermans, first vice president at the Commission, told the minister, Witold Waszczykowski, on the first day of the Munich Security Conference.

The jibe came at the end of a sharp back-and-forth between the two men in which Waszczykowski told Timmermans: "Please allow us to respect our own constitution, not your vision of our constitution. Okay?"

Timmermans retorted that the Venice Commission, a pan-European rights body, had itself accused Poland's conservative government of undermining democracy by crippling its top court.

"Don't believe me, you asked the Venice Commission, they were very clear on their answer. The only thing they got from you was an insulting reply," Timmermans said.

Tensions between Warsaw and Brussels have grown steadily since the eurosceptic Law and Justice (PiS) party swept to power in late 2015 and moved to change the way rulings are made at the top court and to exert more control over state prosecutors.

This prompted the European Commission to open an investigation into the rule of law in Poland. It has given Warsaw two months from December to take steps to protect the powers of its Constitutional Court. Poland has said it will respond later this month.

The EU could in theory freeze Poland's voting rights in the European Union and freeze funds if the government does not allay its concerns. (Reporting by Noah Barkin and Robin Emmott; Editing by Gareth Jones)